Detection of a pair density wave state in UTe₂

Spin-triplet topological superconductors should exhibit many unprecedented electronic properties, including fractionalized electronic states relevant to quantum information processing. Although UTe₂ may embody such bulk topological superconductivity, its superconductive order parameter Δ(k) remains unknown. Many diverse forms for Δ(k) are physically possible in such heavy fermion materials13. Moreover, intertwined density waves of spin (SDW), charge (CDW) and pair (PDW) may interpose, with the latter exhibiting spatially modulating superconductive order parameter Δ(r), electron-pair density and pairing energy gap. Hence, the newly discovered CDW state in UTe₂ motivates the prospect that a PDW state may exist in this material. To search for it, we visualize the pairing energy gap with μeV-scale energy resolution using superconductive scanning tunnelling microscopy (STM) tips. We detect three PDWs, each with peak-to-peak gap modulations of around 10 μeV and at incommensurate wavevectors P_i=1,2,3 that are indistinguishable from the wavevectors Q_i=1,2,3 of the prevenient CDW. Concurrent visualization of the UTe₂ superconductive PDWs and the non-superconductive CDWs shows that every P_i:Q_i pair exhibits a relative spatial phase δϕ ≈ π. From these observations, and given UTe₂ as a spin-triplet superconductor, this PDW state should be a spin-triplet PDW. Although such states do exist in superfluid ³He, for superconductors, they are unprecedented.